1. Field of the Invention
The present invention relates to a planar antenna, and more particularly, to a planar antenna capable of realizing multi-resonance and band widening.
2. Background Art
There is a wideband planar antenna. (For example, see JP-A-2006-033069.) In the planar antenna of JP-A-2006-033069, it is possible to obtain wideband characteristics in which a standing wave ratio is substantially flat between a first resonance frequency of a low frequency side and a second resonance frequency of a high frequency side. The wavelength λ1 of the first resonance frequency of the low frequency side is associated with a dimension A obtained by adding both sides and a short side of a trapezoid of the planar antenna and a relationship of the dimension A=approximately λ1/2 is satisfied.
In the mobile wireless device having the antenna mounted thereon, multi-frequency and band widening are further required. Accordingly, in the planar antenna of JP-A-2006-033069, in order to widen a low frequency band, the dimension A, that is, the length of the sides of the trapezoid, need increase and thus the dimension of the antenna increases.
In the planar antenna of JP-A-2006-033069, the strength against bending is weak. In the arrangement of the coaxial cable, the thickness of the mobile wireless device increases.